1. Field of the Invention
The present invention relates to an optical printer in which an instant film provided with a developer pod is exposed with a fixed exposure head.
2. Description of the Related Art
For example, Japanese Patent Laid-Open Publication Nos. 11-344772 and 11-352595 disclose optical printers in which an exposure head fixed at a predetermined position is driven in synchronism with conveyance of an instant film to print a picture of one frame. In the optical printers described in the above Publications, printing light of each color of R, G and B has a line shape extending in a direction perpendicular to a conveyance direction of the instant film. The printing lights of three colors are simultaneously emitted or are emitted in a line-sequential manner. Meanwhile, by rotating a spreading roller, a developer pod of the instant film is broken to execute a developer-spreading process. In addition, the spreading roller also performs a conveyance process for conveying the instant film.
In such an optical printer, a printing period may be shortened by comparison with a case in that an exposure head is moved for scanning. Further, a space for moving the exposure head is unnecessary so that the optical printer may be downsized.
The optical printers described in the aforesaid Publications employ a rotary encoder in order to measure a conveyance length of the instant film. In virtue of this, the printing light is adapted to be finely adjusted regarding its emission period and its emission intensity. Thus, high-quality printing is performed.
In the above-described optical printer, the spreading roller is driven while printing is performed one line by one line with the exposure head. The developer pod is pressed by the spreading roller to be broken at the beginning of the conveyance of the instant film. A large load is applied to the spreading roller just before breaking the developer pod so that a rotational speed of the spreading roller is suddenly decreased. Right after that, the rotational speed of the spreading roller is suddenly increased. Due to this, a conveyance speed of the instant film is largely changed when the developer pod is broken. The exposure head is required to be driven in synchronism with the conveyance of the instant film. However, when the conveyance speed of the instant film is suddenly increased, it becomes impossible to drive the exposure head in association with the conveyance of the instant film. Thus, there arises a problem in that an unexposed portion is formed to cause a black streak on a printed picture.
The above problem may be solved by improving detection sensitivity of the rotary encoder or by improving an emission changing speed of the printing light and the emission intensity thereof. In another way, the above problem may be solved by starting the exposure after breaking the developer pod. In the former countermeasure, it is required to greatly improve performance of the encoder and the exposure head so that sizes thereof are likely to be enlarged. Further, the cost is likely to be increased.
In the latter countermeasure, it is required that the exposure head and the spreading roller are disposed so as to be adjacent to each other. Consequently, the developer is likely to enter the unexposed surface of the instant film. In order to prevent this, it is considered that the exposure head is slightly moved before starting the conveyance of the instant film. Besides this, it is also considered to reduce a size of a picture to be printed. Doing so, however, causes many disadvantages. In another way, it is considered to decrease the rotational speed of the spreading roller. In this case, however, there is a disadvantage that a printing period is lengthened.
In view of the foregoing, it is a primary object of the present invention to provide an optical printer in which a conveyance speed of an instant film is prevented from changing at the time of breaking a developer pod.
It is a second object of the present invention to provide an optical printer in which a printing process for obtaining a high-quality print is performed, keeping a shortened printing period.
In order to achieve the above and other objects, the optical printer according to the present invention comprises a braking member for preventing a conveyance speed of the instant film from exceeding a prescribed speed.
The instant film is provided with a developer pod and is conveyed by a pair of spreading rollers. An exposure head is disposed so as to be perpendicular to a conveyance direction of the instant film. The exposure head emits a line-shaped printing light in a sequential manner to expose one frame. A conveyance amount of the instant film conveyed by rotating the spreading roller is detected by a conveyance-amount sensor. A print controller monitors a signal outputted from the conveyance-amount sensor to control the exposure head in synchronism with the conveyance of the instant film.
The braking member applies a load to the rotation of the spreading roller or to the conveyance of the instant film. Owing to this, a rotational speed of the spreading roll is prevented from exceeding a predetermined speed so that the conveyance speed of the instant film is prevented from exceeding the prescribed speed.
In a preferred embodiment, the braking member closely comes into contact with the instant film at an upstream side of the spreading roller. The braking member is preferable to be made of an elastic material of a sponge and so forth. Further, the braking member is preferable to have a roller shape rotated in accordance with the conveyance of the instant film.
According to the optical head of the present invention, it is possible to always detect the conveyance amount of the instant film by providing the braking member, although the conventional conveyance-amount sensor is used. The braking member prevents the conveyance speed of the instant film from suddenly changing due to the rupture of the developer pod. In virtue of this, the printing process by which good image quality is obtained may be executed, keeping the shortened printing period.